- From: Martyn Horner <martyn.horner@profium.com>
- Date: Wed, 12 Sep 2001 13:46:22 +0200
- To: pat hayes <phayes@ai.uwf.edu>
- CC: Graham Klyne <Graham.Klyne@MIMEsweeper.com>, w3c-rdfcore-wg@w3.org
Since I contributed last, Pat and Graham have been going at it hammer-and-tongs See: GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0127.html PH: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0130.html GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0131.html PH: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0132.html GK: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Sep/0061.html I am grateful for the attention paid to this question. But, chaps, what I wanted to make was a glossary for the layperson which would help their initial understanding of some of our terms. I see, again, how dubious some of these terms are. Pat knows, from an exchange which came to nothing probably because I didn't express myself that well, that I am concerned about what I call the `temporal coherence' of stuff `on the Web'. This does seem to be an issue and, I can see, it's an issue which will not disappear just by defining (and redefining) the words we use. We have to offer to the newcomer a definition which allows for temporal variance without completely denying the usefulness and significance of the words. For those who haven't been following the thread, much of what has flowed past has been about the validity of defining a resource at all given its changing nature (whether incidentally in a changing world or functionally as a news service, for instance). Graham initially wanted to point out how separated the ideas of entity and resource were as in, for example, `today's weather forecast'. Then the discussion started... Just to quote some of GK's and PH's dialogue: Graham refers me (usefully, thanks) to http://www.w3.org/DesignIssues/Fragment.html where a distinction is made between a fragmentid-less URI which refers to a generic document and a fragmentided URI which refers to an identification within that document (and not just, as we know, a point in that document :-). Thus no '#' suggests just generic access and a '#' suggests an identification (eg, of a resource). Then he says: GK: `I find it difficult to unify the RDF idea of a resource (a thing that is identified) with the general Web idea of a resource (a thing that is queried or accessed) in light of these comments.' Me: So do I, Graham. So do I. I also find it difficult to generalize this distinction to non-document resources (you know the list, people, organisations, trees in the park, numbers,...) GK: (on the time-variance track) `The approach that I have seen adopted is to treat such things as sequences of values, or time-varying functions.' ... `Then, the resource can correspond to the current weather forecast, but its extension includes the set of all weather forecasts for all times; the particular member of that extension one retrieves depends on when the retrieval is performed.' Me: Yes. This is why I think it's important to say that a `resource' is an entity identified by need (if you like), that the act of identifying it as a resource includes an understanding of such characteristics. This may not be its most precise definition but it would suggest for a new reader the role of the concept. PH: `As I understand it, the real-world objects *are* resources, so the idea of being retrievable on the web simply isn't applicable to resources in general.' Me: Retrievability is a characteristic of some resources, of course, but is not the crucial aspect of their identification even if the identity of a resource (`today's weather forecast') is expressed in terms of its retrieval. The resource is identified as `today's weather forecast' and its usefulness (the `need' for identification) is in its timeliness BUT the act of retrieval is not what makes it a resource. GK: `The alternative view I'm trying to offer here is that real-world objects are not resources, per se. In addition to the octet-sequences that are web-retrievable entities, I'm suggesting that the real world objects are (also) part of the resource extension I mentioned previously, rather than the resource directly.' GK: `... but such (time-sensitive) semantics would be part of the semantics of a resource, about which the RDF model theory you have described seems to be agnostic.' Me: Ah-ha! Yes. This is how I think of it. The timeliness of information belongs in the semantic of that information but should not, in some sense, invalidate the identification of it as a resource. Again, a resource is an entity identified as required: the semantics may suggest that the entity will change. PH: `In the meantime however we could also just put this issue off to the future, and the current MT be thought of as kind of instantaneous time-slice of this extended temporal semantics.' Me: Oh, please, no. Or at least, let me get my glossary done with a nice clear message for the newcomer while we perhaps agonize about the real meanings. I don't think we have forced ourselves to consider that RDF refers to `a time-slice of an extended temporal semantic'... The ref (http://www.ietf.org/internet-drafts/draft-masinter-dated-uri-00.txt) that Graham includes is a good one, I admit. The idea of a duri: URN protocol to state that `I am referring to the page as it was then' is, of course, a valid one but it does not fit in with the requirements of a practical Semantic Web. Larry has it right but it's not going to help. It's great for putting in legal documents. However, the Semantic Web is going to have to cope with time-variant data and not just deliberately time-variant (like today's weather) or with time-variance created by retrieval or time-variance due to decay. Help. What shall we tell the novice? `Resource' (and its relationship to `entity') must be in the vocabulary of anyone starting to read the RDF documentation. I'd have thought it completely reasonable that some kernel of meaning can be attached to these words before such a reader has to face that the `true' meaning has certain unclear aspects. Do my definitions suffice, I still wonder... -- Martyn Horner <martyn.horner@profium.com> Profium, Les Espaces de Sophia, Immeuble Delta, B.P. 037, F-06901 Sophia-Antipolis, France Tel. +33 (0)4.93.95.31.44 Fax. +33 (0)4.93.95.52.58 Mob. +33 (0)6.21.01.54.56 Internet: http://www.profium.com
Received on Wednesday, 12 September 2001 07:46:10 UTC